Standards(protocols)

Standards(protocols)

1. application

2. protocol

3. syntax

   • syntax: how msg organized
   • IP packets: w/ header & data field
     • IP: internet protocol
       • connectionless - no need to formally agree to communicate or end the communication
     • 32 bits/row, each row divided into fields
       • #1 field: version number
       • source IP address(32 bits)
       • destination IP address(32 bits)- for routers
       • header checksum: does not send ACK packet - ONLY error detection - IP unreliable
   • UDP datagrams
     • UDP: user datagram protocol. transport layer. no opening, closing, ACK - less traffic than TCP
     • msg called datagram, variable length - 2 headers
       • length - how long the datagram is. variable length
       • checksum - no retrans
     • source port number
     • destination port number
   • Frame: w/ header & IP packet & trailer
     • in data link layer. carry packet
     • measure in octets (group of 8 bits)
     • Eternet II frame
       • not 32 bits/row. instead of in order
       • EUI-48 addresses - 48 bits. others in octets
       • EtherType field - identify IPv4 or 6
       • frame check sequence field - no retrans
   • port number
     • use source port and destination port number fields
     • server - no change
     • client - always change by sessions
   • socket
     • represent IP address & port number, not in the same header. i.e. 60.171.18.22:2707

4. govern msg order

   • msg
     • data field
     • header
       • fields
     • trailer
       • fields
   • HTTP
     • ALWAYS initial by client
     • connectionless - no live connection needed before trans
     • unreliable